A Practical Method to Estimate the Spatial Resolution of GEM Detector

1. A Practical Method to Estimate the Spatial Resolution of GEM Detector Rensheng Wang (王仁生) Tsinghua U. (清华大学) Collaborators: Yan Huang, Zhi-Gang Xiao, Zhao Zhang Rong Wang, HaiyanGao The Fourth Workshop on Hadron Physics in China and Opportunities with 12GeV JLab

2. Outline: • Introduction • Method description • Experimental results • Near future plans • Summary

3. Brief introduction to GEM detector -HV Cathode ~2-30 mm Drift /Sensitive(~1-3kv/cm) GEM1(300v-500v) ~1-2mm Transfer(~1-3kv/cm) GEM2(300v-500v) ~1-6mm Induction(~1-3kv/cm) Anode/Readout strip

4. Introduction to the set up 55Fe • Readout strip: 1-D, width=200um, 400um; • 2-D, width=400um • Preamplifier: Charge-sensitive, 16 channels • DAQ: Based on VME-Bus, peak sensitive ADC

5. General performance

6. Method description

7. Conventional methods for spatial resolution Method Ⅰ: Method Ⅱ: Method Ⅲ : Ref： 1，RADIOLOGY 93: 257-272, August 1969. 2，Med. Phys. 25(1), January 1998 3，Med. Phys. 11(6), 1984

8. Comparison of different methods Ref: Chinese Physics C, Vol. 36, No. 3, Page 228-234 • Difficulties： • Method 1: Precise slit fabrication and alignment in the radiation； • or intense radioactive source； • Method 2: Complex auxiliary equipment； • Method 3: Precise edge fabrication and collimated X-ray source needed;

9. But, what we have: 2, a 55Fe with low Activity (5 × 104Bq), Surface source, s～0.78cm2 1，A slit with adjustable width, but the width can NOT be measured precisely. 3, Very limited in electronics (16 channels); It is natural to use method 1. But…

10. A practical method 55Fe(Surface source) But, the slit width can NOT be measured precisely. Luckily:

11. A practical method (Continue) 55Fe(Surface source) therein, n means the counting rate

12. Simulation Results(1-D) Simulation conditions： GEM spatial resolution：70μm； Slit thickness(mm)：3, 4, 5, 6, 7; Slit width(μm):20,30… 100; The angle(slit with readout strip, deg):1.0, 0.5, 0.25, 0.125;

13. Experimental result • 1-Dimension Readout • Readout strip: D=200um 400um;

14. When W≈40μm: 1, (a): get the events from main peak(mean ±2σ), covered with the red line; 2, (b): calculate the position by the centre-of-gravity method; subtract the background(under the blue dotted line), then fit it with gaus-func; 3, Therein: S-the area of main peak; T-the testing time

15. The Test result(1-D, 200μm readout strip) (1), When w ≈40, 50,60,70,80μm, with the ratio as the x axis, with the σ2tot as the y axis. (2), Fit the graph with line-func, we can get σGEM=56 ±15μm

16. The Test result(1-D, 400μm readout strip) σGEM=41 ±79μm

17. Cluster size of signal of main peak

18. Near Future Plans • Further test: • Position resolution for 2-D detector; • Simulation with Garfield; • Time resolution; • A prototype for SoLID • APV electronics (1024) • Asic-based electronics • Develope the new DAQ ~45cm ~48cm ~20cm

19. Summary • GEM-Detector prototype test is ongoing in our lab; • A new method to evaluate the GEM spatial resolution: • 1) For 1-D and Wreadout=200μm, σgem=56±15μm(1σ); • 2) Global performance tested for the prototype ; • Consistent with literature report • Next step is to build a prototype for SoLID with new electronics and DAQ; Looking forward to the arrival of the GEM foil and the APV electronics Supported by the National Natural Science Foundation of China and Tsinghua University Initiative Scientific Research Program .

20. Thanks！